Our First Specific Aim further develops the concept that sequences of the membrane-active antibiotic Gramicidin S (GS) can be used to deliver biologically active payloads to mitochondria. Specifically, we will construct hybrid molecules with higher catalytic activity than 4-amino-Tempo linked JP4-039 and XJB-5-131. The Second Specific Aim provides molecules linked to NOS inhibitors such as AMT (GS-NOS-I), which will test the hypothesis of Project 1 that mitochondrial targeted small NOS inhibitors will be effective alone and when added to GS-nitroxides as radiation damage mitigators. The Third Specific Aim tests the hypothesis that additive and synergistic effects in radiation mitigation can be accomplished by nanoparticle conjugation of GS-nitroxide and GS-NOS-1 as well as other combination therapeutics. The Fourth Specific Aim will support Project 4 and provide proof-of-principle that hydrogen peroxide (H202) releasing small molecules can induce the formation of high molecular weight oligomers of human (rh)MnSOD with intact activity. This effect of H202 on MnSOD activity is likely due to the oligomerization-induced stabilization of the enzyme's structure. Therefore, it can be used as a protective strategy to replenish irradiation induced MnSOD deficiency. The Fifth Specific Aim is directed toward the synthesis of triphenylphosphonium (TPP)-derived oximes, nitroxides, salen-Mn and porphyrin-Mn complexes and thus employs a charge-driven delivery strategy of radioprotective agents to mitochondria. The Sixth Specific Aim is focused on the synthesis of general analogs of Project lead structures, the development of structure-activity relationships of all drug and lead candidates, and the gram-level scaleup of any other synthetic compounds in any ofthe Projects and non-synthetic Cores ofthe Pittsburgh CMCR. Specifically, Core D will optimize PUMA inhibitors in collaboration with Project 5, and optimize delivery systems in collaboration with Cores C and E.